Starting up procedure for the synthesis of hydrocarbons



Aug. 12, 1958 s. D. SUMERFQRD ETAL 7 2,847,438

STARTING UP PROCEDURE FOR THE SYNTHESIS OF HYDROCARBONS Original FiledNov. 12, 1948 CONDENSER REACTOR I j 20 y.- 7 1 I l l l I I CATALYSTINLET a i i rff'ii L 27 :J c 9 5 3' 2.- ==I+ 2 1 6A5 LINE INLETSEPARATOR N w t I PREHE'ATER 0.4 0.4 l l a F. I I I 2 COMPRESSORS Thepresent invention relates to-the catalytic conversion of ca'rbon oxideswith hydrogen to' for rnihydriocar- -bons and valuable oxygenatedorganic compounds. More particularly, the invention relates to .animproved method of placing the conversion catalyst on stream to startthe conversion process. Thepresent application is a di- .visi on of ourco-pendipg application ,Serial Number 59,462, filedNovemher 1 2, 1948,now abandoned.

Ih inveh .will b u y un er t od frQm th -foll i sdet le e e iptie en thacc m anyin d The synthesis of hydrocarbons and other valuable productsfrom gas mixturescontaining various proportions ob-hydrogen and carbonoxides, particularly c ihencmoih s de i shed, moving shed, a ..we.l s in:d n

'sphe ifluidre talys ope at o is .well in the ;Th tque i mandharaete mof.ithe ynthetic product de- :1 e .1 la ely th temperatures, pressur Hzratios of the feedgas, and the type of catalyst used, the latter lbeingusually an iron group -metal catalyst -;promoted-With such promoters asvarious -alkali metalcornpounds, rare earth -meta1 oxides, 'ma'gnesia,alumina, and/ or other compounds in amounts of about: 05-10%.

' For example, cobalt supported on an inert-carrier and United StatesPatent 0 promoted with -thoria and/or -magnesiarnay;be-used in-combinatio n with relatively low fpressu'res- (atmospheric to ab ut S'atmospheres), lowtemperatures (about 375- 425 R) and high'-H /CO;ratiosof'2' or more to produce a-substantially saturated hydrocarbon material}from which valuable diesel jfuels, lubricating-oils and waxes may be"obtained. Iron-type catalysts "usually -promoted witha suitable'alkalimetal compound such a's the chlorides or fluorides, carbonates, oxides,phosphates nitrates, acetates, etcr-of potassium or sodium may be'usedin com- "bination with relatively high pressures (about 5-50attnospheres), --high temperatures (.about -500750 R) and low HzCO-ratios of not --abovew2,-to produce '-a predominantly unsaturatedmaterial from which large proportions of high octane motor fuels may berecovered. Whi1e theipresentinvention isiapplicableto all;types ofsynthesis operation; outlined-above, it isv ofgreatest value .whenapplied tothe dense phase fluid =type pr,o,ce.dure using iron-typecatalysts. :This type of operation;;i nvolves passing the synthesis gasupwardly through a ,dense turbulent mass of finely divided iron catalystlfluidizedby the reacting gases 'and gasiform reaction products toresemble a boilingliquid having'a well defined upperlevel.

,Fresh synthesis metal catalysts are usually prepared by decomposing'the"corresponding -meta1 carbonyls or by reducing the corresponding metaloxides with hydro- ;gen attemperatures of about S OOP- 1600 F.. andatmospheric or elevated pressures, specific conditions dependingpnthetypeo f catalystinvolved. All catalysts-so prepared have an extremelyhigh initial activity for the highly exothermic synthesis reaction. Asaresultserious difiieul sh v been-en oun er gdur ns zth te i ep Periodof the p enehtieu rlywit rre ne t emreaetor in an atmosphere {,Q bYdIQ Q13n -,h ete l-it' Patented Aug. 12, 1 958 ice perature control. Forexample, when a freshly prepared iron -catalyst is contacted with -freshsynthesis gas at synthesis conditions in a-react or equipped with heatwith- -drawal --means -normally sufficient to carry oif the heat evolvedby the synthesis reaction, thetemperature may rise within a very shorttime of, say, one or two hours several hundred'degrees above optimumreaction-temperatures. Such high temperatures are conducive ;to' anexcessive formation of free'carbon which is deposited omthe catalyst andwhich detrimentally affects the active life and general utility ofthecatalyst for-the synthesis reaction. Whilethis istrue to a certainextent for all types of synthesis operations, it has the-most. seriousefiects on the dense phase type fluid operation using'iron,cata- -lysts.

Proper fiui'dization whichdetermines failure or success of fluidoperation depends :largely on {a :proper particle size .distribution:throughout :the dense catalyst phase. :More particularly, the powdered.catalyst must .not. convtain ;apreponderance ofrparticle fineszhaving-al sizeifrorn :0-20.microns or the phase density will drop toapoint atWhiCh allcatalyst is reventuallytblown.tout.of the re- .actor. All ironcatalysts have .a marked tendency to disintegrate .under .the heavymechanical stresses of'fluid operation. "This :tendency isconsiderablyincreased by the deposition ofvcarbononzthe.catalyst. 'Itwill beappreciated, therefore, i that .if "the reaction temperature-..and withi it. carbontforrnation are. not earefully controlled -duringath .early :stages of :t-he r-lsynthesis, :catalystfiisin- .tegrationmay rbecome -so pronounced even during -the starting period. thatinoperative. conditions are .encountered .atter on-stream periods of.uneconomically short :dutatio'n. Thezpresent invention; overcome t iidiflieulty.

{It is, a therefore, :the, principal, obieebofithe ;pre se nt in-:vention toqprovide .meansflforlcontrolling the ternpera re .during atheinitial tstages of the catalytic ,.-synthesis of hydrocarbons from.carbon oxi des -and; hydrogen.

-A.= more specific, object; ofjhe invention, is t o provide ,an

improved start g-1 p procedur f r dens whos fluid c t y typ hydrocarbonyn hesi :epehat en tue iron-type 1 catalysts.

i m-i bj c andzed e ta es wi ppea hereihatter- :In accordanc w th th prsen in ention tire h y t educted-.isy.11 h si cat ly i placed it i th sn hes the ,,-de.sir. p rat n ;;p ssh :1 ltem eh h r a eas os y .pp aehi;g op imum i yh si em eratur wher up th hydr e a mo h r i eplac i d siredat henc bu '.;p. .fe -a y i l il e ement with {the 5 1 111 6 3 a ve e 5b1 per od of t me until the synthesis gas j in t-hereactor is. undiluted,with extraneeusihy r h Deneadinsen l pe-R em ;di. i.on, th eeher e .e:th .e el st and h e g and '.de.s.ign f :th reactor, Zth timeelame f m htar of synthesis gas feeduntil the reactor contains. undiluted syn hesia :$.1 ld'b fib l 1 -r 1 $lQl glt fiQ hei rnotzh r fh 1 the e er t e .The siha brewgem-atmosphere-acts as, a, diluent. reducing the{ total,lheat rele s v nt e ui brium eendi ieh h tw e the re ea e an h a t ra ahav .be n eaehedresult, we a. hat-du in th rting Perio la oid d- .I eeeh i h .pr t r edethhedimente th veh e th reactor is eharsed wth.mwdueedeathlrst.t 'd etien-hfit c ta i ee rie t ut insithvw t hy h es hitahl rr dh ti eehd fiens efltemne et r an sure ;until the ,waterformation QeaSes' temperature and pressure are thenadjusted to. those-.desirahle for the synthei -,:PI e While I e i h s.th hyd n steed-shethereaffite hehyd s hfee re la n adflmnihi easeme t a'with n e t m ofabo L.2 .h u. until-u ces's conel lut d; s n h si .se l tf .lwherei enttthe .1

perature may be reduced, after catalyst reduction is completed, to alevel slightly below that of synthesis operation whereby the initialheat release may be further buffered.

When carried out in this manner, the starting-up procedure of theinvention permits perfect temperature control during the first criticalhours of the synthesis process, particularly in dense phase fluid typeoperation using irontype catalysts.

Having set forth its objects and general nature, the invention will bebest understood from the following more detailed description in whichreference will be made to the drawing which illustrates schematicallyone type of apparatus suitable for carrying out the invention.

Referring now in detail to the drawing, reference numeral 1 designates aconventional fiuid type synthesis reactor provided with a gasdistributing means such as grid 3, a gas feed line 5, a catalyst supplyline '7, and a heat exchange means such as coil 9. When starting up theprocess, unreduced synthesis catalyst of fiuidizable particle size isadmitted to reactor 1 through line 7. Simultaneously an inert gas suchas nitrogen is supplied from line 2 via preheater 4 and line 5. Theinert gas may be preheated in heater 4 to any temperature sufficient topreheat the catalyst in reactor 1 to the desired reduction temperatureof about 6001400 F. The heating effect of the inert gas may be aided bypassing a suitable heating medium such as hot flue gases, steam,mixtures of diphenyl with diphenyl oxide, etc. through coil 9.

The superficial linear velocity of the inert gas entering reactor 1through grid 3 is so adjusted that the catalyst in reactor 1 forms adense turbulent mass of solids resembling a boiling liquid having a Welldefined upper level L. The gas leaves reacor 1 through line 11. Thecatalyst supply through line 7 may be discontinued when level L hasreached a predetermined elevation. The conditions required for properfluidization are well known in the art. For the purposes of thisdescription it is sufficient to note that for most iron-type catalyststhese conditions include particle sizes of -200 microns, mostly -100microns, superficial gas velocities of about 0.3-2 ft. per second andapparent bed densities of about 50-150 lbs. per cu. ft.

When the catalyst has reached substantially the desired reductiontemperature and all the air is replaced by nitrogen, hydrogen issupplied in place of nitrogen through line 2 and heater 4, and reactor 1is placed under the pressure desired for catalyst reduction. Thispressure is preferably atmospheric but may range up to about 400 lbs.per sq. in. The hydrogen feed rate is so controlled that properfluidization velocities are maintained at a hydrogen space velocity ofabout 1000-2000 v./v./hr. Under these conditions reduction may becompleted within about 4-10 hours, as determined by the absence of waterin the gas leaving through line 11.

Thereafter the temperature in reactor 1 is decreased to the desiredtemperature for synthesis operation or about 10 to 150 F. belowsynthesis temperature, say to about 420 to 600 F., and the pressure israised to a suitable synthesis pressure which lies for iron-typecatalysts between about 150 and 600 lbs. per sq. in., preferably between200 and 500 lbs. per sq. in. Now, the hydrogen supply through line 2 isreplaced in steadily or periodically increasing proportions by synthesisgas containing H and CO in the ratio of about 0.5-321 supplied bycompressor 15 via line 17 and preheater 4 which is now so controlled topreheat the synthesis gas to about 300 -500 F. Simultaneously, a coolingmedium such as steam, mixtures of diphenyl with diphenyl oxide, etc. ispassed through coil 9 to absorb the heat released by the exothermicsynthesis reaction now setting in. The feed rate of synthesis may beincreased at the expense of free hydrogen feed in such a manner thatfull synthesis gas feed rate and an undiluted synthesis gas atmospherein reactor 1 are obtained after about 5-20 hours of operation and theoptimum synthesis temperature of, say, about 500-650 F., is notsubstantially exceeded during this time until normal operatingconditions are established. In the case of iron catalysts, for instance,synthesis gas may be first cut in at a rate of about 10% to 20% of thefinal operating rate and this rate may be increased by about 10% to 20%of the final rate every 1 to 2 hours.

Upon the start of the conversion reaction, synthesis products areWithdrawn through line 11 and passed to a conventional product recoverysystem of which merely a condenser 20 and a liquid-gas separator 25 areshown. A portion of the total product in line 11 and/or of the gasseparated in separator 25 may be recycled to reactor 1 via lines 29 and27, respectively, in any manner known in the art. It will also beunderstood by those skilled in the art that a heating and cooling jacketmay be provided around react-or 1 to take the place of coil 9 if thereactor diameter is too small to permit proper fiuidization in thepresence of a heat exchange coil. Other modifications obvious to theexpert are within the scope of the invention.

The invention will be further illustrated by the following specificoperating examples.

EXAMPLE I A conventional fluid-type synthesis reactor was charged withan oxidized iron catalyst containing 78% iron, 20% copper, and 0.5%potassium and 1.5% impurities such as silicon and aluminum, calculatedon an oxide basis,

and having a particle size distribution as follows:

.The catalyst had a bulk density of 1.33 grams per cc.

Reduction was carried out with H in situ as described above for 4 hoursat atmospheric pressure, a temperature of 673 F., a hydrogen feed rateof 1100 standard volumes of H per volume of unfiuidized catalyst perhour and a superficial linear gas velocity of 0.3 to 0.4 ft. per second.Thereafter the temperature was reduced to 475 F. and a synthesis gashaving an H :CO ratio of 1 was cut in the hydrogen feed, at a feed rateof about 40 v./v./hr., and recycle (cold) was started at a ratio ofabout 10. Within the next 4 hours, the fresh synthesis gas feed rate wasincreased by about 110 v./v./hr. and the H feed correspondinglydecreased until a fresh undiluted synthesis gas feed rate of 480v./v./hr. was reached, whereupon the process was continued in a normalmanner. Temperature control during the starting-up period wassatisfactory and no fluidization difiiculties due to carbon formationwere encountered.

EXAMPLE II An iron material containing 92% Fe, 0.5% NaCO and 7.5%impurities was used as the starting material. This material had a bulkdensity of 2.4 grams per cc. and a screen analysis as follows:

Percent On mesh 13.0 On mesh 4.5 On 200 mesh 34.2

On 325 mesh Through 325 mesh 48.3 100.0

The material was oxidized with a mixture of air and nitrogen to 16.6% 0in 21 hours at 11001200 F. prior to charging to the synthesis reactor.Thereafter the material was charged to the reactor and treated thereinas follows: y

(1) Reduction with H for 8 hours at 228 v./v.hr., 677 F. and atmosphericpressure.

(2) Circulation of H during 27 hours leakage test at 550 F. and 300 p.s. i. g.

(3) Synthesis gas cut into the system filled with H, at 550 F. and 300p. s. i. g. The synthesis gas had a 1.1:1 H /CO ratio and was free of CThe feed velocity of the gas was 0.3 ft. per second, the feed rate 230v./v./hr., and the ratio of recycle/fresh feed was 11, tail gas beingused for recycle.

(4) The H in the system was displaced from the reactor over a period ofabout 18 hours. Thereafter the process continued at the conditions soestablished. No fluidization difficulties were encountered during thestarting-up period above described.

While the foregoing description and exemplary operations have served toillustrate specific embodiments of the invention, they are not intendedto be limiting in scope. Other modifications may appear to those skilledin the art without departing from the spirit of the invention.

What is claimed is:

1. In the synthesis of hydrocarbons by contacting a bed of ironsynthesis catalyst with a total feed gas consisting of a synthesis gasconsisting of hydrogen and carbon monoxide in a mol ratio of not above2.0:1 and recycled gas comprising a fraction of the products of thereaction at a superatmospheric synthesis pressure and an elevatedreaction initiation temperature of above about 420 F. in a synthesisunit comprising a catalytic reaction zone and a liquid product recoveryzone in which said recycled gas is separated from the product gasesformed in the catalytic reaction zone, the method of starting up theunit which comprises pressuring the unit with a gas consisting ofhydrogen to said superatmospheric synthesis pressure, circulating saidgas consisting of hydrogen in said unit comprising said catalyticreaction zone and said liquid product recovery zone at said reactioninitiation temperature and said superatmospheric synthesis pressure at arate suflicient to maintain the catalyst in the fluidized state, then,while maintaining the unit at said superatmospheric synthesis pressureby controlling the introduction of hydrogen, introducing synthesis gasinto the circulating hydrogen in advance of said catalytic reaction zoneat an increasing rate controlled to maintain the temperature of thecatalyst in the reaction zone below about 650 F. while recycling reactoreffluent until the fresh feed to said unit consists of said synthesisgas, and continuing the introduction of synthesis gas into said unit inan on-stream period during which hydrocarbons are synthesized.

2. A method in accordance with claim 1 in which said reaction initiationtemperature is within the range of about 420 F. to about 600 F.

3. A method in accordance with claim 2 in which said iron synthesiscatalyst is at least partially reduced from the oxide.

References Cited in the file of this patent UNITED STATES PATENTS2,244,196 Herbert June 3, 1941 2,437,051 Sensel et al. Mar. 2, 19482,445,795 Millendorf July 27, 1948 2,461,570 Roberts Feb. 15, 19492,483,512 Voorhies, et a1. Oct. 4, 1949 2,527,846 Phinney et a1 Oct. 31,1950 2,533,694 Safiord Dec. 12, 1950 2,541,677 Summerford et a1. Feb.13, 1951 2,666,077 McGrath Jan. 12, 1954 2,691,033 Easly et al. Oct. 5,19 54

1. IN THE SYNTHESIS OF HYCROCARBON BY CONTACTING A BED OF IRON SYNTHESISCATALYST WITH A TOTAL FEED GAS CONSISTING OF A SYNTHESIS GAS CONSISTINGOF HYDROGEN AND CARBON MONOXIDE IN A MOL RATIO OF NOT ABOVE 2.3:1 ANDRECYCLED GAS COMPRISES A FRACTION OF THE PRODUCTS OF THE REACTION AT ASUPERATMOSPHERIC SYNTHESIS PRESSURE AND AN ELEVATED REACTION INITITATIONTEMPERATURE OF ABOVE ABOUT 420*F. IN A SYNTHESIS UNIT COMPRISING ACATALYST REACTION ZONE AND A LIQUID PRODUCT RECOVERY ZONE IN WHICH SAIDRECYCLED GAS IS SEPARATED FROM THE PRODUCT GASES FORMED IN THE CATALYSTREACTION ZONE, THE METHOD OF STARTING UP THE UNIT WHICH COMPRISESPRESSURING THE UNIT WITH A GAS CONSISTING HYDROGEN TO SAIDSUPERATMOSPHERIC SYNTHESIS PRESSURE, CIRCULATING SAID GAS CONSISTING OFHYDROGEN IN SAID UNIT COMPRISING SAID CATALYST REACTION ZONE AND SAIDLIQUID PRODUCT RECOVERY ZONE AT SAID REACTION INITIATION TEMPERATURE ANDSAID SUPERATMOSPHERIC SYNTHESIS PRESSURE AT A RATE SUFFICIENT TOMAINTAIN THE CATALYST IN THE FLUDIZED STATE, THEN, WHILE MAINTAINING THEUNIT AT SAID SUPERATMOSPHERIC SYNTHESIS PRESSURE BY CONTROLLING THEINTRODUCTION OF HYDROGEN, INTRODUCING SYNTHESIS GAS INTO THE CIRCULATINGHYDROGEN IN ADVANCE OF SAID CATALYTIC REACTION ZONE AT AN INCREASINGRATE CONTROLLED TO MAINTAIN THE TEMPERATURE OF THE CATALYST IN THEREACTION ZONE BELOW ABOUT 650*F. WHILE RECYCLING REACTOR EFFLUENT UNTILTHE FRESH FEED TO SAID UNIT CONSISTS OF SAID SYNTHESIS GAS, ANDCONTINUING THE INTRODUCTION OF SYNTHESIS GAS INTO SAID UNIT IN ANON-STREAM PERIOD DURING WHICH HYDROCARBONS ARE SYNTHESIZED.